Two recent observations in our laboratory, the enhanced stability of 2'-O-methylated synthetic RNA molecules towards a specific nuclear nuclease and the demonstration of methylnucleosides in Novikoff tumor cell messenger RNA, suggest a possible role of mRNA methylation in the regulation of genetic expression. The distribution and characterization of methylnucleosides in cytoplasmic mRNA and nuclear mRNA precursors will be determined in tumor and transformed cells and compared to normal cells. Messenger RNA from each cell type will be purified and enzymatically degraded to nucleosides. Methylnucleosides will be resolved by high-speed liquid chromatography. The role of methylation in the processing of mRNA sequences will be studied by observing mRNA processing under conditions which modify RNA methylation. Cells grown in culture under limiting methionine concentrations as well as the addition of several known inhibitors of RNA methylation will be used in an attempt to inhibit mRNA processing. Synthetic RNA molecules containing low levels of 2'-O- methylnucleosides will be employed as substrates for a 3'- exoribonuclease purified from Novikoff nuclei. Other synthetic RNA molecules containing 2'-O-methylnucleosides in specific positions within the polymer will be used to detect other RNA processing enzymes and to further define the role of 2'-O-methylation in RNA processing. The role of poly(A) sequences in RNA processing and nuclear transport will be studied in vitro in isolated nuclei. Nuclear release of pre-labeled RNA will be used to determine the effect of several RNA inhibitors, suspected of interfering with poly(A) attachment or function, on the role of poly(A) in nuclear release.